Oda Bultum university college of Natural and computational Science

Department of Physics

ODA BULTUM UNIVERSTY

COLLEGE OF NATURAL AND COMPUTATIONAL
SCIENCE
DEPARTMENT OF PHYSICS
TITLE: TO DETERMINE PHOTOELECTRIC EFFECT IN SOME ELEMENT

PREBERD BY: -

Takele Eba ______________IDNO 2819/13

March, 2016 E.C

Chiro, Ethiopia
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Declaration

I declare that the senior project is our original work and has not been presented for a
degree in any other university.
Indivdual
Takele Eba
This senior project has been submitted for examination with my approval as
university advisor.

Advisor Name Signature Date

Acknowledgment
First of all, I would like to introduce great thanks for our God that has helped us in
every difficult condition. And then we would like to express our deep thanks and
gratitude to our advisors Mr.Fantahun T. for their day to day encouraging support and
guidance in carrying out the Research. The other person we kindly say to thank are
our instructor for that we are voluntarily helping us to provide some information what
can help us to prepare this research.

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Acronyms And Abbreviations

E= energy of photon
Na= sodium
K = potassium
Cs = cesium
Ag = sliver
pt = platinum
f = incidence frequency
V =stopping potential

= Work function

f= threshold frequency
C =speed of light

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Abstract
This study was designed to experimentally evaluate what happen to the metal atom
after takes place photoelectric effect, the Photoelectric effect was accidentally
discovered by Heinrich Hertz in 1887.this paper provides a better understanding of
the concept of photoelectric effect important senior project issues in this burgeoning
area of photoelectric effect. Classical and modern view of photoelectric effect. To
identify the photoelectric effect regarding to the experiment I used to the visible
wavelength photoelectric effect from 460-635 NM.
Explain photoelectric effect at some heave element (Cs, Ca,Pt,Na, to examine the
relation between stopping potential and kinetic energy. The work function is
increasing, the photoelectric effect is decreased.

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List of Table

Table 1 heavy element of photoelectric effect .....................................................10

Table 2 experimental data record........................................................................17
Table 3 experimental result in photoelectric effect.............................................21

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List of Figure
Figure 1 : Representation of Photoelectric effect....................................................7
Figure 2 Internal Photoelectric Effect.....................................................................8
Figure 3 -External photoelectric effect....................................................................8
Figure 4 photoelectric effect with KE and work function....................................11
Figure 5 Effects of Intensity of Incident Radiation on Photoelectric Effect.......12
Figure 6 For constant frequency and different intensities.....................................22

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Table Of Content
Acknologment-------------------------------------------------------------------------------II
Acronyms And Abbreviations-----------------------------------------------------------III
Abstract-------------------------------------------------------------------------------------IV
Chapter One---------------------------------------------------------------------------------------3
1. Introduction------------------------------------------------------------------------------------3
1.1 Background of the study--------------------------------------------------------------3
1.2 STATEMENTE OF PROBLEME--------------------------------------------------4
1.3 RESEARCH QUESTION-----------------------------------------------------------4
1.4 Objective of Study----------------------------------------------------------------------4
1.4.1 General objective----------------------------------------------------------------4
1.4.2 Specific objective----------------------------------------------------------------4
1.5 Significant of study---------------------------------------------------------------------5
1.6 Scope of the study----------------------------------------------------------------------5
1.7 Limitation of the study-----------------------------------------------------------------5
Chapter two : Review literature----------------------------------------------------------------6
2.1 Photoelectric effect---------------------------------------------------------------------6
2.1.1 Classical point of view on photoelectric effect------------------------------6
2.1.2 Modern point of view on photoelectric effect-------------------------------6
2.2 Types of Photoelectric Effect---------------------------------------------------------7
2.2.1 Internal Photoelectric Effect---------------------------------------------------7
2.2.2 External Photoelectric Effect--------------------------------------------------8
2.3 Minimum Condition for Photoelectric Effect---------------------------------------9
2.3.1Threshold Frequency (γth)------------------------------------------------------9
2.3.2 Threshold Wavelength (λth)---------------------------------------------------9
2.4 Laws of Photoelectric Emission-----------------------------------------------------10
2.5 photoelectric effect at some heave element----------------------------------------10
2.6 Factor Affecting of Photoelectric effect--------------------------------------------11
2.6.1 Intensity of incident radiation------------------------------------------------11
2.6.2. Effects of Potential Difference between metal plate and collector-----12
2.7 APPLICATION OF PHOTOELECTRIC EFFECT------------------------------13
2.7.1The Photo Cell------------------------------------------------------------------13
Chapter Three :Methodology-----------------------------------------------------------------16
3.1 studying Area--------------------------------------------------------------------------16
3.2 Methodological approach-----------------------------------------------------------16
3.3 Technical Sample or Data Collection----------------------------------------------16
3.4 METHDOLOGICAL DATA ANALYSIS AND DISCUSSION --------18
CHAPTER FOUR : RESULTE ,CONCLUSSION and RECOM MONDETION- -19
4.1 EXPERMENTAL RESULT--------------------------------------------------------19
CONCLUSION----------------------------------------------------------------------------23
RECOMENDETION---------------------------------------------------------------------24
Reference-----------------------------------------------------------------------------------25

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CHAPTER ONE
1. INTRODUCTION
1.1 Background of the study
Like most modern science, the photoelectric effect was accidentally discovered by
Heinrich Hertz in 1887 during the course of the experiment that discovered radio
waves [1]. It remainder explained until 1905 when Albert Einstein postulated the
existence of quanta of light which, when absorbed by an electron near the surface of a
material, could give the electron enough energy to escape from the material [2] .
Robert Millikan carried out a careful set of experiments, extending over ten years that
verified the predictions of Einstein’s photon theory of light. Einstein was awarded the
1921 Nobel Prize in physics[3]: "For his services to Theoretical Physics, and
especially for his discovery of the law of the photoelectric effect." Millikan received
the Prize in 1923 for his work on the elementary charge of electricity (the oil drop

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experiment) and on the photoelectric effect. Hertz died (at age 36) before the first
Nobel Prize was awarded[4]. In the photon explanation of the photoelectric effect,
photons, carrying an energy hfcan free electrons from the surface of a material if the
photon energy is greater than the work function of the material. The work function is
the minimum energy required to release an electron from the material. When an
electron in a material absorbs a high enough Energy photon, it gains enough kinetic
energy to escape from the substance. This is called the photoelectric effect. Einstein’s
theory predicts that the kinetic energy E of the electron once it has escaped from the
material is directly proportional to the photon's frequency. The Stopping Potential is
the potential difference applied to stop the electrons being ejected from the surface
when the light falls on it. The stopping voltage refers to the voltage difference that is
required to stop the electrons from moving across the metal plate in the photoelectric
effect.
The photoelectric effect1 helped to solidify the notion of light as quanta. drawing
from Planck's quantum hypothesis for black body radiation, that light has energy
quanta, Einstein extended it to explain how the interaction of light with electrons of a
metal give rise to photo electrons. Photoelectric theory explains why and how the
velocity of the electrons, and thus the measured voltage, varies with frequency and
not light intensity. The photoelectric effect cannot be explained on the basis of
electromagnetic theory. When frequency is increased the energy of individual photons
increases. The work function is fixed. Hence, the any increase in the energy of
individual photons results in increase in maximum kinetic energy of the ejected
electrons.
This photoelectric effect becomes the basic concept of solar power generation. In
other words, when light is emitted above a certain frequency, electrons pop out
immediately.
1.2 Statement of Problem
It is obviously known that photo electric effect because of given evidence the
different scholar. The first owner the photoelectric effect was explained in 1905 by
A. Einstein. Einstein reasoned that if Planck’s hypothesis about energy quanta was
correct for describing the energy exchange between electromagnetic radiations. But
when a photon hits an electron and thereby knocks it out of the atom into the 'void',
what not happens to the metal atom? So, our concern to identify or give some clue of
the metal atom after takes places photoelectric effect in visible wavelength (450-650)

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NM by experiment.
1.3 Research Question
This study will concern about limitation and success photoelectric when incident light
hit the metal. It will attempt to answer the following basic question:
 How affect photoelectric effect in heavy element?
 What happen photoelectric effect when frequency is increase?
 What happen photoelectric effect when the wave length is increase?
 What is the relationship b/n the stopping potential and kinetic energy?
1.4 Objective of Study
1.4.1 General objective
To investigate the concept of photoelectric effect.
1.4.2 Specific objective
 To express what happen to the metal atom after takes place photoelectric effect.
 To explain photoelectric effect at some heave element.
 To identify what happened photoelectric effect depends on frequency and
wavelength.
 To determine kinetic energy in heavy element.
1.5 Significant of study
Study of this senior project had been significant to provide knowledge about which
metal or elements are maximum the photoelectric effect takes places and identify
metal element, which is minimum work function in order to maximize photoelectric
effect.
It gives deep understand for all who want to know about theoretical concept and
experimental way of photoelectric effect.
1.6 Scope of the study
This senior project sweeps out to understanding photoelectric effect with in some
heavy element, in visible wavelength range of 460-635nm.
1.7 Limitation of the study
During this senior project is not as such easy task, there are a lot of ups and down,
some of these are: -
Lack of experience about the conducting of the project
Time constraint
Lack of internet access

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CHAPTER TWO

REVIEW LITERATURE

2.1 Photoelectric effect

Photoelectric effect is the process of emitting the electrons from the a metal surface

when the metal surface is exposed to an electromagnetic radiation of sufficiently high

frequency happens when light hits the meta electrons are knocked off atoms, causing

electricity to flow (2).

2.1.1 Classical point of view on photoelectric effect

The classical understanding of physics, when light shines on a surface, it slowly

transfers energy into the substance. This increases the kinetic energy of the particles
until finally, they give off excited electrons. This process is called thermal emission
and it was considered the most likely explanation for the photoelectric effect. Given
this justification, it was expected that increasing light intensity regardless of
frequency would result in photo electrons with higher kinetic energies. In addition,
since the substance must first reach a critical temperature before it can begin ejecting

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electrons, it was expected that the photoelectric effect would not be observed
immediately [5].
2.1.2 Modern point of view on photoelectric effect

The photoelectric effect is a phenomenon in which electrons are ejected from the
surface of a metal when light is incident on it. the ejected electrons are called photo
electrons. It is important to note that the emission of photo electrons and the kinetic
energy of the ejected photo electrons is dependent on the frequency of the light that is
incident on the metal’s surface. The process through which photo electrons are ejected
from the surface of the metal due to the action of light is commonly referred to
as photo emission [6]. The photoelectric effect occurs because the electrons at the
surface of the metal tend to absorb energy from the incident light and use it to
overcome the attractive forces that bind them to the metallic nuclei. to be more
precise, light incident on the surface of a metal in the photoelectric effect causes
electrons to be ejected. The electron ejected due to the photoelectric effect is called a
photo electron and is denoted by e–. The current produced as a result of the ejected
electrons is called photoelectric current [7].

.
Figure 1: Representation of Photoelectric effect [2].

2.2 Types of Photoelectric Effect

We have learned what photoelectric effect is and also discussed some important types
of the photoelectric effect. The photoelectric effect is basically divided into two types:
2.2.1 Internal Photoelectric Effect

The discharge of electrons within the object when photons strike the surface of the
metal is known as an internal photoelectric effect.

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The collection of all the energy levels of the valence electrons is termed as a valence
band. When photons make contact with the metal surface, some of the valence
electrons which are lower energy level electrons obtain an ample amount of energy
and are unbound from the parent atom. They further transmit into the higher energy
level conduction band, where the electrons move freely from one region to another.

Figure 2 Internal Photoelectric Effect

This emission of photo-electrons inside the material is termed internal photo-emission

or internal photoelectric effect. The internal photoelectric effect is also called the
photo conductive effect or photovoltaic effect. The photovoltaic effect is the principle
utilized behind the working of solar panels.
2.2.2 External Photoelectric Effect

The discharge of electrons from the surface of the metal, when photons strike the
metal surface, is known as the external photoelectric effect.

Figure 3-External photoelectric effect

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As shown in the above figure (3), when the light hits the surface of the metal, certain
valence electrons and free electrons acquire enough energy to detach from the
bonding with the metal and are emitted from the metal surface. The external
photoelectric effect happens when the frequency of the incident light is larger than the
work function or threshold energy of a metal.
When the energy of the photon is equivalent to the energy and kinetic energy required
to eradicate an electron, it is known as the photoelectric effect equation. The
mathematical form of the photo electric effect equation is expressed as follows:
hν=+E………………………………………… (2.1)
2.3 Minimum Condition for Photoelectric Effect

2.3.1Threshold Frequency (γth)

It is the minimum frequency of the incident light or radiation that will produce a
photoelectric effect, i.e., the ejection of photo electrons from a metal surface is known
as the threshold frequency for the metal. It is constant for a specific metal but may be
different for different metals.
If γ = Frequency of the incident photon and γth= Threshold frequency, then,
If γ < γTh, there will be no ejection of photo electron and, therefore, no photoelectric
effect.
If γ = γTh, photo electrons are just ejected from the metal surface; in this case, the
kinetic energy of the electron is zero.
If γ > γTh, then photo-electrons will come out of the surface, along with kinetic
energy.
2.3.2 Threshold Wavelength (λth)

During the emission of electrons, a metal surface corresponding to the

greatest wavelength to incident light is known as threshold wavelength.
λth = c/γth
For wavelengths above this threshold, there will be no photoelectron emission. For λ
= wavelength of the incident photon, then
If λ < λTh, then the photoelectric effect will take place, and ejected electron will
possess kinetic energy.
If λ = λTh, then just the photoelectric effect will take place, and the kinetic energy of
ejected photoelectron will be zero.
If λ > λTh, there will be no photoelectric effect.

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2.3.3 Work Function or Threshold Energy (Φ)

The minimal energy of thermodynamic work that is needed to remove an electron
from a conductor to a point in the vacuum immediately outside the surface of the
conductor is known as work function/threshold energy.
Φ = hγth = hc/λth
The work function is the characteristic of a given metal. If E = energy of an incident
photon, then
If E < Φ, no photoelectric effect will take place.
If E = Φ, just a photoelectric effect will take place, but the kinetic energy of ejected
photo-electron will be zero
If E > photo-electron will be zero
If E > Φ, the photoelectric effect will take place along with the possession of the
kinetic energy by the ejected electron.
2.4 Laws of Photoelectric Emission

There is no time lag between the irradiation of the surface and the ejection of the
electrons. At a particular fixed frequency of incident radiation, the rate of the
emission of photo electrons i.e., the photo current increases with increase in the
intensity of the incident light. Photo electric effect does not occur at frequency less
than threshold frequency (4).

At the frequency above the kinetic energy of the ejected electrons depends only on
the frequency of the exposed radiation and not on its intensity[].
2.5 photoelectric effect at some heavy element

Table 1 heavy element of photoelectric effect

Metal Pt Ag Na K Cs Ca
Work function 6.4 4.7 2.3 2.2 1.9 2.9

We can analyze the frequency relationship using the law of conservation of energy.
The total energy of the incoming photon, E photon must be equal to the kinetic energy
of the ejected electron, KE electron, plus the energy required ejecting the electron
from the metal. the energy required to free the electron from a particular metal is also
called the metal's work function, which is represented by the symbol Φ\Phi (in units
of J ):

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The mathematical expression of the energy of photon:

E =KE + Φ …………………………..(2.2)
But, KE=eV
Then, the kinetic energy is given as:
KE=E-Φ ,since Φ=hfo
KE=hf-hfo
KE=h(f-fo) ………………….(2.3)
Almost the work function is decrease when goes to a group from top to down.
The work function is increasing, the photoelectric effect is decreased.
So, we can calculate the max of KE.
For example
For pt KE=(10-6.4)J=3.6J.
The work function is increasing, the photoelectric effect is decreased.

Figure 4 photoelectric effect with KE and work function

2.6 Factor Affecting of Photoelectric effect

2.6.1 Intensity of incident radiation

The frequency of incident light and intensity is kept constant and the potential
difference between the plates is varied. Keeping the intensity and frequency of light
constant, the positive potential of C is increased gradually. Photoelectric current
increases when there is a positive increase in the potential between the metal plate and
collector up to a characteristic value.

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For a given photo metal if the frequency and applied voltage is kept constant with
increasing intensity then we observe that photo current increases with increases in
intensity without change in the stopping potential[9].

Figure 5 Effects of Intensity of Incident Radiation on Photoelectric Effect

2.6.2. Effects of Potential Difference between metal plate and collector

The intensity and voltage across the plates is kept constant for a photo metal with
change in frequency of the incident light. The stopping potential is measured for
different frequencies. The graph is drawn between frequencies versus stopping
potential. The frequency at which the photo current begins is called threshold
frequency. This is the minimum frequency for photo electric effect to occur. There is
no change in photoelectric current when potential is increased higher than the
characteristic value for any increase in the accelerating voltage [10].
This maximum value of the current is called saturation current. For a given photo
metal if the frequency and intensity of incident light kept constant and if the potential
difference between the plates is increased then photo current also increases until it
reaches a maximum (saturated) value. If the terminals are reversed and we increase
the potential difference gradually then photo current decreases and at one point it
becomes zero. The Stopping Potential is the potential difference applied to stop the
electrons being ejected from the surface when the light falls on it. The stopping
voltage refers to the voltage difference that is required to stop the electrons from
moving across the metal plate in the photoelectric effect.
This point where the current is zero is Stopping Potential [11].
2.7 Application of Photoelectric Effect

2.7.1 The Photo Cell

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Basically, the photocell is one kind of resistor, which can be used to change its
resistive value based on the light intensity. These are inexpensive, simple to obtain in
numerous sizes as well as specifications. Each photocell sensor will perform directly
compare with other modules, even if they’re from the same family. Actually, the
changes in this can be higher, large, etc. Because of these reasons, they cannot be
used to decide exact light levels within mill candela otherwise lux. This article
discusses an overview of the photocell which includes working, circuit diagram,
types, and its applications [12] .
A photocell can be defined as; it is a light-sensitive module. This can be used by
connecting to an electrical or electronic circuit in an extensive range of applications
like sunset to sunrise lighting that mechanically turns on whenever intensity of light is
low. These are also used in other applications like intruder alarms and also automatic
doors [13] .
The application of the phenomenon of photo electric cell a vacuum tube in which
electric current will flow when light strikes the photo sensitive cathode. Photo cells
are sensors that allow you to detect light. They that reason they often appear in toys,
gadgets and applications. They are often refers to a cell/ they are made cadmium
sulfide[14] .
Generally, the photoelectric cell has wide range of applications some of these are:
A) Automatic switching arrangement of street light (turn on and off automatically)
B) Automatic fire alarm
C) Automatic controls the temperature of a furnace.
D) Automatic door system
E) Security system
F) Automatic Burglar Alarm
In this case continuous light is incident on photoelectric cell, if any how it get
disturbed it Produces sound i.e. alarm.
G) Reproduction of sound in cinema film.
H) Exposure meters correct time of exposure.
I) Scanner
J) In paper industry
K) In astronomy
L) To determine the opacity
M) To locate flaws and holes in the finished goods

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N) Photometry

CHAPTER THREE

METHODOLOGY
Methodology refers to the overarching strategy and rationale of our project. It
involves studying the methods used in our field and the theories or principles behind
them, in order to optimize an approach that matches our objectives. In which we
describe the actions, took to investigate and project a problem and our rationale for
the specific processes and techniques we use within our project to identify, collect and
analyze information that helps you understand the studying of the problems.
3.1 studying Area
Oda Bultum university in the Department of Physics in Optics and Laser laboratory
class.
The study was conducted at Oda Bultum university Jalo campus which is situated in
chiro 326 kms away from the capital of Ethiopia.
3.2 Methodological approach

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The study of the general approach to inquire a given field is quantitative. Quantitative
data is, quite simply, information that can be quantified. It can be counted or
measured, and given a numerical value. Such as a given wavelength to measured
3.3 Technical Sample or Data Collection
Experimental Record: -for Experimental Record data our research project entry for an
experiment recording all data and pertinent details of an experiment, such that a peer
could repeat it. for studies that include more than one experiment, several experiments
can be part of one record (under one study ID). our collect data on events that have
already happened. Retrospective studies are generally less expensive and take less
time than prospective studies, but are more prone to measurement error. So, we used
retrospective method. set up the apparatus and checked the power supply.
Monochromatic light from the source of sufficiently short wavelength enters the tube
through quartz window and falls on photosensitive plate C which acts as an emitter.
Slid light source to 250mm position, turned on the power, preheat the system for 5
minutes, and set current multiplier at x0.001 position.
Placed different color (blue(460nm), Green(500nm), Yellow(540nm),orange(570nm)
and red(635nm)) or varying the frequency and switched on the intensity set at a
particular value.
Put the voltage direction in the reverse bias (in the negative) and then by adjusted the
voltage at 0v observe the photo current value from the display mode.
Increased slowly the reverse applied voltage up to the current (µA) is zero and note
down (take) the stopping (threshold) voltage for each frequency.
Set the intensity at a particular value with a fixed colour and then note down the
Photo current up to zero when the applied reverse voltage is starting from zero with
the interval of 0.05v.
Changed only the intensity and the same step like procedure 5 and take the reverse
voltage and photo current.
Put the intensity at a particular value (but it greater than that used in step 6 ) and use a
given color (example orange)or fixed frequency and then take the photo current by set
reverse voltage started from zero with the interval of 0.05 up to the photo current is
zero.do this twice by different colour in the same step.
Experimental Data
Table 2 experimental data record
Color Valve of Stopping potential Kinetic energy

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wavelength (nm) (mv) (kE)

Blue 460 1.01
Green 500 0.82
Yellow 540 0.68
Orange 570 0.48
Red 635 0.31

3.4 Methodological Data Analysis and Discussion

Analysis presented here shows that:
Quantitative data analysis from that obtain several iterative or trials or phase are;
Depend on table two to determine the kinetic energy.
Work Function is the minimum amount of energy necessary for the photoelectric
emission to start and it varies from material to material.
The work function is defined as the minimum amount of energy, that is necessary to
free the electron.

CHAPTER FOUR

RESULTE, CONCLUSSION AND RECOM MONDETION

4.1 Experimental Result

KE, max kinetic energy.
h = Planck's constant
E = Energy of photon
E=KE thus, hf=KE+hf
Hf-hf=KE where f-f =f.
Hf =KE but h=eV/f
So, ( eV/f)/f = KE
ev =KE
Where, e =1.6 x 10^-19 c, which is the basic unit of elementary charge electron.
For trial, the stopping potential v= 1.01m v
ev = KE
KE= 1.6 x 10^-19 x 1.01x10^-3 ev
= 1.616x10^-22J

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For trail two the measured stopping potential v,=0.82v

Then KE =ev
=1.6 x 10^-19 x0.82ev
=1.312x10^-3 x10^-19cv
= 1.312 x 10^-22J
For trial three stopping potential is 0.68 x10^-3 c.
Then KE= 1.6 x10^-19 x0.68 x10^-3
=1.85 x10^-22J
For trial four, the measured stopping potential is 0.49.
Then KE =ev
KE =1.6 x10^-19 x 0.49 x10 ^-3cv
= 0.789 x10^-22J
For trial fife,the measured stopping potential is 0.31 x 10^-3c.
Thus the KE = ev
KE = 1.6 x 10^-19 x0.31 x 10^-3cv.
=0.496 x10^-22J
And-also to analysis the frequency of a given wavelength
For blue color, the frequency(f) =speed of light© /wavelength(L)
F=c/L
F = 3 x10^8m/s
4.6 x10^-7m

=6.52 x10^14Hz
For green color , f =3x10^8m/s
5x10^-7m
F= 6x 10^14Hz
For the yellow color,
F =3x 10^8m/s
5.4x 10^-7m
=5.3 x10^14
For orange color ,the frequency f
F = 3x10^8m/s
5.7 x10^-7m
=5.2 x10^14Hz.

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For red color ,the frequency f

F =3x10^8m/s
6.35x10^-7m
=4.7x10^14Hz.
For some heavy metal (Ag,Na,Cs,Pt,K) of the relationship work function and
photoelectric effect express below the following .
Photoelectric effect at some heavy element;
Let the incident light of photon E = 10J
Then for platinum(pt) E = KE +Φ
KE = E -Φ
KE = (10 -6.4)J =3.6J
For sliver (Ag) KE=(10- 4.7)J=5.3J
For sodium (Na) KE= (10-2.3)J=7.7J
For potassium(K) KE=(10-2.2)=7.8J
For cesium (Cs) KE =(10-1.9)=8.1J
Table 3 experimental result in photoelectric effect
Color Wavelength Frequency (HZ) Stopping Kinetic energy(J)
(NM) potential(mv)
Blue 460 6.52 x10^14Hz 1.01 1.616 x10^-22
Green 500 6x 10^14Hz 0.82 1.312 x10^-22
Yellow 540 5.3 x10^14 0.68 1.85 x10^-22
Orange 570 5.2 x10^14Hz. 0.49 0.789x10^-22
Red 635 =4.7x10^14Hz. 0.31 0.496 x10^-22
Figure 6 For constant frequency and different intensities.

This graph lezare new ….mr, techeger elgni

Graph tomorrow we will try…

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The Stopping Potential is the potential difference applied to stop the electrons being
ejected from the surface when the light falls on it. The stopping voltage refers to the
voltage difference that is required to stop the electrons from moving across the metal
plate in the photoelectric effect.
When experiments were performed to look at the effect of light incident and
frequency, the following results were observed:
The kinetic energy of photo electrons increases with light frequency.
The kinetic energy of photo electrons remains constant as light intensity increases.
The work function is increasing, the photoelectric effect is decreased
The element after takes place the photoelectric effect is not changed.
An element is determined by the number of protons in the nucleus, not the number of
electrons. So, a metal atom losing electrons will not change what the element is.

CONCLUSION
Under this senior project we have been understand about photoelectric effect within
the relationship between stopping potential and kinetic energy. When light shines
metal surface, electrons is emitted, the emission of electron on this surface is called
photoelectric effect, and the emitted electron is called photo electron. A material that
can exhibit the photoelectric effect is said to be photo e missive. A surface is exposed
to electromagnetic radiation above a certain threshold frequency typically visible
light, near ultraviolet for other metals, and extreme ultraviolet for non-metals the
radiation is absorbed and electrons are emitted. Experimentally, while the number of
emitted photo electrons increases with the incident light intensity, the maximum
kinetic energy of the emitted photo-electrons is observed to be independent of the
intensity but does depend on the frequency. The intensity of incident light is kept
fixed and the wavelength is increased, and also the frequency and stopping potential
are the decreased. The photoelectric effect is increased when the work function is
decreased.
photoelectric current remains the same. Photoelectric effect is applicable for
industries, photo cells, photovoltaic cells, and etc.

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RECOMENDETION
We are curious about the photoelectric effect and cannot explain myself a couple
phenomenon. If the someone will conduct this experiment first to know the name of
the material at optics and laser physics lab. because in order to calculate the work
function.

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Department of Physics

Reference
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Department of Physics

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